Multilayer, white, laser-cuttable and laser-inscribable polyester film

Abstract

The invention relates to a white, coextruded, oriented polyester film with a base layer (B) and with at least one outer layer (A), where the base layer (B) includes a whitening pigment and/or void-forming incompatible polymer at a concentration of from 2 to 35% by weight (based on the weight of the base layer (B)), and from 0.01 to 15% by weight (likewise based on the weight of the base layer (B)) of a pigment that absorbs laser energy. The invention further relates to a process for production of these films and to their use as laser-cuttable and laser-inscribable film.

1. A white, coextruded, oriented laser-cuttable polyester film comprising a base layer (B) and at least one polyester outer layer (A), wherein the base layer (B) comprises a whitening pigment and/or void-forming incompatible polymer at a concentration of from 2 to 35% by weight, based on the weight of the base layer (B), and from 0.1 to 15% by weight, based on the weight of the base layer (B), of a pigment that absorbs laser energy and
 said outer layer (A) ranges in thickness from 0.4 to below 20 microns, and said outer layer (A) comprises less than 0.5% by weight of pigment that absorbs laser energy. 
 
     
     
       2. The polyester film as claimed in  claim 1 , wherein the outer layer (A) comprises a whitening pigment and/or void-forming incompatible polymer which is identical with or different from the whitening pigment and/or incompatible polymer in the base layer (B). 
     
     
       3. The polyester film as claimed in  claim 1 , wherein the whitening pigment is titanium dioxide, calcium carbonate, barium sulfate, zinc sulfide, zinc oxide, or a mixture comprised of one or more of these pigments. 
     
     
       4. The polyester film as claimed in  claim 1 , wherein the base layer (B) comprises a whitening pigment and void-forming incompatible polymer and the entire amount of white pigment and incompatible polymer in the base layer is not more than 35% by weight and is not less than 2% by weight. 
     
     
       5. The polyester film as claimed in  claim 1 , wherein the pigment that absorbs laser energy is in the form of coated particles, and the coating comprises a material that absorbs laser energy. 
     
     
       6. The polyester film as claimed in  claim 1 , wherein the outer layer (A) comprises less than 0.5% by weight of pigment that absorbs laser energy and from 0.05 to 18% by weight, based on the weight of layer (A) of whitening pigment and/or void-forming incompatible polymer. 
     
     
       7. The polyester film as claimed in  claim 6 , wherein the outer layer (A) comprises 0% by weight of pigment that absorbs laser energy. 
     
     
       8. The polyester film as claimed in  claim 1 , wherein said film exhibits a whiteness of greater than 60. 
     
     
       9. The polyester film as claimed in  claim 1 , wherein said film exhibits a transparency of less than 60%. 
     
     
       10. The polyester film as claimed in  claim 1 , wherein said film exhibits a longitudinal and transverse shrinkage at 200° C. of less than 10%. 
     
     
       11. The polyester film as claimed in  claim 1 , wherein said film exhibits an elongation or tensile strain at 100° C. of less than 3%. 
     
     
       12. The polyester film as claimed in  claim 1 , wherein said film exhibits a longitudinal and transverse modulus of elasticity of greater than 3000 N/mm 2 . 
     
     
       13. The polyester film as claimed in  claim 1 , wherein said film exhibits longitudinal and transverse F5 values of greater than 80 N/mm 2 . 
     
     
       14. A process for producing a polyester film as claimed in  claim 1  comprising
 (i) compressing a polyester polymer or a polyester polymer mixture for the individual layers of the film in an extruder and plastifying the polymer or polymer mixture to form melts, 
 (ii) shaping the melts in a coextrusion die to form flat melt films, 
 (iii) mutually superposing and pressing the flat melt films through a flat-film die and 
 (iv) drawing off the superposed and pressed flat melt films on a chill roll and on one or more take-off rolls to form a prefilm, 
 (v) biaxially stretching the prefilm, 
 (vi) setting the biaxially stretched prefilm, and 
 (vii) relaxing the set prefilm to form film, 
 wherein the polyester polymer of the base layer (B) comprises a whitening pigment and/or void-forming incompatible polymer at a concentration of from 2 to 35% by weight, based on the weight of the base layer (B), and of from 0.1 to 15% by weight, based on the weight of the base layer (B), of a pigment that absorbs laser energy. 
 
     
     
       15. Laser cuttable and laser-writable film comprising film as claimed in  claim 1 . 
     
     
       16. The polyester film as claimed in  claim 1 , wherein said film ranges in thickness from 10 to 100 microns. 
     
     
       17. The polyester film as claimed in  claim 1 , wherein said base layer (B) is formed from polyester selected from polyethylene terephthalate; polyethylene 2,6-naphthalate; polyethylene 2,6-naphthalate bibenzoate; polyethylene isophthalate or mixtures thereof and said outer layer (A) is formed from polyethylene terephthalate. 
     
     
       18. A white, coextruded, oriented laser-cuttable entirely polyester film comprising a base layer (B) and at least one outer layer (A), wherein the base layer (B) comprises a whitening pigment and/or void-forming incompatible polymer at a concentration of from 4 to 35% by weight, based on the weight of the base layer (B), and from 0.1 to 15% by weight, based on the weight of the base layer (B), of a pigment that absorbs laser energy,
 wherein said outer layer (A) has a thickness ranging from 0.75 microns up to below 100 microns and comprises 
 (i) less than 0.5% by weight of pigment that absorbs laser energy and 
 (ii) from 0.05 to 4% by weight of a whitening pigment and/or void-forming incompatible polymer 
 said film exhibiting a longitudinal and transverse shrinkage at 200° C. of less than 6% and a longitudinal and transverse modulus of elasticity of greater than 3500 N/mm 2 , and an expansion at 100° C. of less than 3%. 
 
     
     
       19. The polyester film as claimed in  claim 1 , wherein said film can be cut with a Nd:YAG laser with 1064 nm emission wavelength at speeds of from 10% to 35% higher than comparable white films. 
     
     
       20. The polyester film as claimed in  claim 1 , wherein said base layer (B) comprises a whitening pigment and/or void-forming incompatible polymer at a concentration of from 8 to 35% by weight, based on the weight of the base layer (B), and said film exhibits a longitudinal modulus of elasticity of greater than 3000 N/mm 2 .